using expand=true in Solr SynonymFilterFactory?

Question

Solr doc explains the role of expand=true in SynonymFilterFactory as the followings:

a synonym will be expanded to all equivalent synonyms. 
If it is false, all equivalent synonyms will be reduced to the first in the list. 

I am wondering what it means exactly? If someone could elaborate on what it does, it will be great.

Answer 1

From the Solr SynonymFilterFactory documentation on the Solr Wiki:

 # If expand==true, "ipod, i-pod, i pod" is equivalent to the explicit mapping:
 ipod, i-pod, i pod => ipod, i-pod, i pod

 # If expand==false, "ipod, i-pod, i pod" is equivalent to the explicit mapping:
 ipod, i-pod, i pod => ipod

Since Solr SynonymFilterFactory is now deprecated, the SynonymGraphFilterFactory class is now used. This answer still holds true for SynonymGraphFilterFactory.